The humoral and cellular immune systems respond vigorously to HIV-1 infection but do not prevent the inexorable progression of the disease. The investigators believe the result of exposure to native HIV-1 envelope glycoproteins (env) is a disordered immune response. They propose that as a consequence, antibody responses are impaired or biased. Biases in antibody responses can be manifested in several ways as a result of different mechanisms. They will focus on antibody constant region usage which effects the isotype and class of the antibodies within the repertoire. They propose: (1) that constant region (isotype and class) significantly affects antibody function, epitope binding, env conformational changes, and neutralization and (2) that constant region usage among antibodies to native env during natural infection is biased or inappropriate. Inappropriate constant region usage is predicted to reduce the efficacy of the humoral response and contribute to the early loss of control of the disease and eventual progression. They will use human monoclonal antibodies (HMAB) to study these hypotheses by constructing isotype and class switched variants of the HMAB (chHMAB). A group of 9 HMAB representing diverse neutralizing epitopes and an enhancing epitope have been selected for study. chHMAB will be constructed, purified and studied. A chHMAB will be constructed, purified and studied. They will be using a series of carefully chosen assays and tests to identify differences in isotype/class functions. Several tests in each category are necessary because of different limitations of the assays. They will compare binding and kinetics with env glycoproteins on native virions, cell surfaces and by surface plasmon resonance. Env mutants will be studied to identify structural features related to differences in kinetics and binding. The comparative ability of chHMAB variants to neutralize or promote HIV-1 infection of T cell lines, PHA blasts and macrophages will be studied. The functional capability of the chHMAB to mediate ADCC, complement/antibody dependent enhancement of binding, and cell mediated cytotoxicity will be studied. They will use sera from highly defined patients to affinity purify isotype/class specific antibody to clinically relate our results and study natural immunity in the normal host. The applicants believe that it is important to identify protective immune responses and to optimize the protection provided by these responses in light of the difficulty natural protective processes have in neutralizing HIV-1. Being able to direct the humoral immune response into an optimal configuration may be extremely important in developing a highly effective vaccine.